The plate count is no longer considered the only test for the bacterial count of milk. There has recently been a tendency for the methylene-blue, or even the recently developed resazurin test, to displace the colony count as a measure of hygienic quality. Many workers, however, after experience with the dye reduction tests, have returned to the plate count, especially for advisory work, and consider that the new simple tests give inadequate information. Moreover, the plate count is still considered the best test for pasteurized milk. The questions of cost and availability of medium constituents, therefore, assume considerable importance in wartime.

Two media (Min. Health, 1937; Min. Agric. 1934) have received official recognition in England for routine plate counts of milk. Both media (yeastrel agar and milk agar) contain 0·5% peptone, so that a considerable amount can be used if a large number of samples is tested. A shortage of peptone has already been experienced and the price has increased by over 100%. Experiments were therefore undertaken to find an alternative satisfactory medium containing less peptone.